Rebecca and Emma Harper, both 17, died when the barn at Uckington, near Cheltenham, Gloucestershire, became an 'inferno'.
The three men, David Harper (not related), 20, and Wisdom Smith and Daniel Winter, both 19, pleaded not guilty at Bristol Crown Court to two joint charges of manslaughter and one of arson, all on 24 January last year.
Mr Harper, who escaped the blaze with the other two men, allegedly told police: 'We thought the girls would get out the back.'
But he later added: 'We did not know if the girls got out. We were worried to death about the girls.'
Mr Harper, from Uckington, told Detective Sergeant Alen Gibb during interviews that after drinking with the girls in a pub the three men took them to the barn by taxi.
He eventually said he had lit a bundle of straw to see what he was doing while having sex with Rebecca.
'I put it out, then I smelled smoke. Obviously it did not go out. The fire started when I lit that little thing,' he said.
Mr Harper said he smelled smoke while having sex with Rebecca. 'It was really bad. It was getting in my eyes. I got up and Becky got up. She was looking for her tights. That is the last time I spoke to her,' he said.
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